The catalytic ring opening of naphthenic molecules in the upgrading of heavy crude oils is a preferred reaction for improving the cetane number of the diesel fraction. Contrary to other upgrading options such as hydrogenolysis and cracking of hydrocarbons, catalytic ring opening is a selective reaction, cleaving the naphthenic ring only once to avoid a reduction in the number of carbon atoms per molecule. However, not all selective ring opening reactions produce an equivalent upgrading effect. That is, when ring opening occurs at unsubstituted carbon-carbon bonds, the octane number is improved in the gasoline fraction, while ring opening at substituted carbon-carbon bonds improves the cetane number of the diesel fraction.
Catalytic selective ring opening in heavy oil upgrading has been studied using both single-ring compound models like methylcyclopentane (MCP) and methylcyclohexane, as well as with multiple-ring compound models such as indan, decalin, tetralin, naphthalene, and phenanthrene, etc.
Platinum group metals are known to selectively catalyze the ring opening of naphthenes, and most ring opening catalysts therefore contain platinum as the major component. Platinum metal—based catalysts are currently used in various middle distillate upgrading processes. The majority of these monometallic or bimetallic catalysts (containing another transition or post-transition metal) are prepared using traditional methods—that is, via support impregnation with molecular precursors of the desired active component(s). As such, traditional synthesis of Pt—Sn/SiO2 or Pt—Bi/SiO2 catalysts for use in dehydrogenating paraffins has been previously described, for example in U.S. Pat. No. 3,511,888. Another example, described in U.S. Patent Application Publication No. 2007/0062848, discloses a process to treat a feed with a high portion of aromatic compounds with two or more fused aromatic rings. The catalysts proposed include one or more metals selected from the group of Pd, Rh, Ru, Ir, Os, Cu, Co, Ni, Pt, Fe, Za, Ga, In, Mo, W or V deposited preferably on zeolites via ion exchange or impregnation. Methods typically used in generating these catalysts result in polydispersed metal nanoparticles, which consume expensive metals in catalytically unfavorable size and structure modes.
Generally, the activity and selectivity of catalysts depends on the type of metal, metal particle sizes, and the nature of the supports. Recent breakthroughs have allowed the production of metal nanoparticles with controlled size and shape, however the final structure, properties, and behaviour of these catalysts depends strongly on synthesis conditions and metal nature. Moreover, it appears that knowledge gained regarding the synthesis conditions and nanoparticle structure effective in the preparation of one particular type of catalyst may not be readily transferable to the preparation of other types of catalysts. Accordingly, guidance regarding the reliable synthesis of nanoparticle catalysts having a consistent and reproducible size, structure and chemical composition has not been available for the particular application, and catalytic behaviour cannot necessarily be predicted.
For example, U.S. Pat. No. 6,090,858 describes the generation of cubic, tetrahedral, and polyhedral platinum group nanoparticles formed in the presence of a capping agent. Palladium and ruthenium monometallic nanoparticles have been formed, however the conditions for formation of each of these nanoparticles are distinct, and the utility of these monometallic nanoparticles is not definitely known a priori. Suitable reaction conditions can be found only by extensive experimentation.
The literature regarding stabilized bi- and tri-metallic nanoparticles shows that, likewise, these particles may be generated by following well known colloidal chemistry techniques. However, each catalytic application requires its own optimized combination of metals and nanoparticle structure modes. Some references describe the use of Pt, Pd, R, Ir, and mixtures thereof, and some include a second component selected from Sn, Re, Ge, Pb, As, Sb, W, Os, Cd, In, Ti, P, Ga, Ru, Ca, Mg, Ba, Sr. However, the best performance in the literature has been achieved using platinum as the major component (see, for example, U.S. Pat. No. 7,655,137, which describes a Pt—Re catalyst, and U.S. Pat. No. 7,569,508, which describes a Pt—Sn catalyst). Across the field of catalyst literature, bimetallic catalyst activity and selectivity strongly depend on nanoparticle size, structure, and chemical composition. Thus, the teachings of the literature cannot easily or predictably be applied across the range of intended species to provide a desired catalytic behaviour.